Gasoline dithering for spark-ignited gaseous fuel internal combustion engine

ABSTRACT

An internal combustion engine system of the present application includes a spark-ignited internal combustion engine that is powered by a gaseous fuel. The engine system also includes an exhaust system that is in exhaust gas receiving communication with the internal combustion engine. The exhaust system includes an exhaust treatment component. Additionally, the exhaust system includes a liquid fuel injection system in liquid fuel injecting communication with the exhaust system to inject liquid fuel into exhaust gas upstream of the exhaust treatment component.

FIELD

This disclosure relates to spark-ignited gaseous fuel internalcombustion engines, and more particularly to an exhaust system thatdithers an liquid fuel for such internal combustion engines.

BACKGROUND

Emissions regulations for internal combustion engines have become morestringent over recent years. Environmental concerns have motivated theimplementation of stricter emission requirements for internal combustionengines throughout much of the world. Governmental agencies, such as theEnvironmental Protection Agency (EPA) in the United States, carefullymonitor the emission quality of engines and set acceptable emissionstandards, to which all engines must comply. Generally, emissionrequirements vary according to engine type. Emission tests forspark-ignited gasoline (e.g., aqueous or non-gaseous fuel) enginestypically monitor the release of carbon monoxide, nitrogen oxides (NOx),and unburned hydrocarbons (UHC). Catalytic converters (e.g., oxidationcatalysts) implemented in an exhaust gas aftertreatment system have beenused to eliminate many of the regulated pollutants present in exhaustgas generated from gasoline powered engines. For example, some knownthree-way catalysts include carefully selected catalytic materialformulations to specifically oxidize carbon monoxide and unburnedhydrocarbons, and reduce nitrogen oxides to less harmful components,present in the exhaust gas. Conventional three-way catalysts aredesigned to oxidize or reduce such pollutants more efficiently forengines running above the stoichiometric air-to-fuel ratio (i.e., richconditions).

Recently, due at least in part to high crude oil prices, environmentalconcerns, and future fuel availability, many internal combustion enginedesigners have looked to at least partially replace crude oil fossilfuels, e.g., gasoline and diesel, with so-called alternative fuels forpowering internal combustions engines. Desirably, by replacing orreducing the use of fossil fuels with alternative fuels, the cost offueling internal combustion engines is decreased, harmful environmentalpollutants are decreased, and/or the future availability of fuels isincreased. Known alternative fuels include gaseous fuels or fuels withgaseous hydrocarbons, such as, for example, natural gas, petroleum gas(propane), and hydrogen. The combustion byproducts present in exhaustgas generated by spark-ignited gaseous-powered engines are similar tothose present in exhaust gas generated by spark-ignitednon-gaseous-powered engines. Accordingly, conventional gaseous-poweredengine systems utilize the same or similar oxidation catalysts found innon-gaseous-powered engine systems to oxidize the regulated pollutantsgenerated by gaseous-powered engines.

Traditionally, gaseous-powered engines are operated at rich air-to-fuelratios (e.g., richer than stoichiometric) in order to reduce oxygenconcentrations within the exhaust gas, and thus the formation of carbonmonoxide and nitrogen oxides. However, lower oxygen concentrations inthe exhaust gas may fail to adequately replenish oxidation catalystsconfigured to store oxygen for NOx reduction purposes.

Additionally, operating a gaseous-powered engine under stoichiometric orricher air-to-fuel ratios results in a relatively low brake thermalefficiency of the engine. Operating at such air-to-fuel ratios causeshigh combustion temperatures, which result in high componenttemperatures in the engine, and the necessity to reduce output power toavoid component failure. However, in view of the premium placed onsatisfying exhaust emissions regulations, conventional gaseous-poweredengines are designed to meet exhaust emissions regulations at theexpense of thermal efficiency and power density.

Finally, many internal combustion engine systems experience long delaysbetween a cold start of the engine and the exhaust gas reachingtemperatures necessary for efficient reduction of NOx in the exhaustgas.

SUMMARY

The subject matter of the present application has been developed inresponse to the present state of the art, and in particular, in responseto the problems and needs in the art that have not yet been fully solvedby currently available exhaust systems for gaseous-powered internalcombustion engines. Accordingly, the subject matter of the presentapplication has been developed to provide an exhaust system for agaseous-powered engine that overcomes at least some shortcomings ofprior art systems. For example, in some embodiments described herein, anexhaust system for a gaseous-powered engine dithers an aqueous or liquidfuel, such as gasoline, into the exhaust system for NOx reductionpurposes to allow the engine to run leaner (e.g., with a higherair-to-fuel ratio, such as greater than 1.0) compared to conventionalsystems, which results in an increase in the thermal efficiency andpower density of the engine. Additionally, in certain embodimentsdescribed herein, the dithering of liquid fuel into the exhaust systempromotes a faster increase in exhaust gas temperature after a cold startthan conventional systems.

According to some embodiments, an internal combustion engine system ofthe present application includes a spark-ignited internal combustionengine that is powered by a gaseous fuel. The engine system alsoincludes an exhaust system that is in exhaust gas receivingcommunication with the internal combustion engine. The exhaust systemincludes an exhaust treatment component. Additionally, the exhaustsystem includes a liquid fuel injection system in liquid fuel injectingcommunication with the exhaust system to inject liquid fuel into exhaustgas upstream of the exhaust treatment component.

In certain implementations of the internal combustion engine system, thegaseous fuel is natural gas. In yet some implementations, the liquidfuel is gasoline.

According to some implementations of the internal combustion enginesystem, the liquid fuel injection system injects liquid fuel into theexhaust gas based on an air-to-fuel ratio of the exhaust gas generatedby the spark-ignited internal combustion engine. The spark-ignitedinternal combustion engine may generate exhaust gas with an air-to-fuelratio above 1.0.

In some implementations, the exhaust treatment component stores oxygen,and the liquid fuel injection system injects liquid fuel into theexhaust gas based on an oxygen storage capacity of the exhaust treatmentcomponent. Alternatively, or additionally, the liquid fuel injectionsystem injects liquid fuel into the exhaust gas during a cold start ofthe spark-ignited internal combustion engine.

The exhaust system of the internal combustion engine, in someimplementations, includes an exhaust manifold that is coupled to thespark-ignited internal combustion engine. The liquid fuel injectionsystem can inject the liquid fuel into the exhaust manifold.

According to certain implementations, the engine system also includes agaseous fuel injection system that is in gaseous fuel injectingcommunication with the spark-ignited internal combustion engine. Theliquid fuel injection system can be configured to inject liquid fuelinto the exhaust gas independently of the injection of gaseous fuelinjected into the engine by the gaseous fuel injection system. Thequantity and timing of the injection of liquid fuel into the exhaust gasby the liquid fuel injection system may be based solely on conditions ofthe internal combustion engine system downstream of the spark-ignitedinternal combustion engine.

The exhaust treatment component is an oxidation catalyst in someimplementations, a three-way catalyst in some implementations, and anitrogen oxide reduction catalyst in yet some implementations. Theliquid fuel injection system is a retrofitted diesel exhaust fluidinjection system in some certain implementations. The gaseous fuel canbe substantially solely natural gas.

According to another embodiment, an electronic control module for aspark-ignited internal combustion engine powered by a gaseous fuelincludes an exhaust system condition module that determines a conditionof an exhaust system in exhaust gas receiving communication with thespark-ignited internal combustion engine. The electronic control modulecan also include a liquid fuel control module that commands thedithering of a liquid fuel into the exhaust system based on thecondition of the exhaust system.

In some implementations of the electronic control modules, the exhaustsystem includes an oxidation catalyst, and the condition of the exhaustsystem includes an oxygen storage capacity of the oxidation catalyst.The condition of the exhaust system can be an air-to-fuel ratio ofexhaust gas generated by the spark-ignited internal combustion engine incertain implementations. The condition of the exhaust system can be anexhaust gas temperature below a minimum threshold in yet someimplementations.

According to yet another embodiment, a method for dithering a liquidfuel into an exhaust system in exhaust receiving communication with aspark-ignited internal combustion engine powered by a gaseous fuel isdisclosed. The method includes determining a condition of the exhaustsystem, and injecting a liquid fuel into exhaust gas flowing through theexhaust system based on the condition of the exhaust system.

The described features, structures, advantages, and/or characteristicsof the subject matter of the present disclosure may be combined in anysuitable manner in one or more embodiments and/or implementations. Inthe following description, numerous specific details are provided toimpart a thorough understanding of embodiments of the subject matter ofthe present disclosure. One skilled in the relevant art will recognizethat the subject matter of the present disclosure may be practicedwithout one or more of the specific features, details, components,materials, and/or methods of a particular embodiment or implementation.In other instances, additional features and advantages may be recognizedin certain embodiments and/or implementations that may not be present inall embodiments or implementations. Further, in some instances,well-known structures, materials, or operations are not shown ordescribed in detail to avoid obscuring aspects of the subject matter ofthe present disclosure. The features and advantages of the subjectmatter of the present disclosure will become more fully apparent fromthe following description and appended claims, or may be learned by thepractice of the subject matter as set forth hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the advantages of the subject matter may be more readilyunderstood, a more particular description of the subject matter brieflydescribed above will be rendered by reference to specific embodimentsthat are illustrated in the appended drawings. Understanding that thesedrawings depict only typical embodiments of the subject matter and arenot therefore to be considered to be limiting of its scope, the subjectmatter will be described and explained with additional specificity anddetail through the use of the drawings, in which:

FIG. 1 is a schematic diagram of an internal combustion engine systemhaving an exhaust system that dithers a liquid fuel according to oneembodiment;

FIG. 2 is a schematic diagram of an electronic control module of aninternal combustion engine system;

FIG. 3 is a schematic diagram of an internal combustion engine systemhaving an exhaust system with a three-way catalyst and a gasolineinjector that dithers gasoline into the exhaust system according toanother embodiment; and

FIG. 4 is a schematic flow chart diagram of a method for retrofitting anexisting exhaust system if necessary and dithering a liquid fuel intothe exhaust system according to one embodiment.

DETAILED DESCRIPTION

Reference throughout this specification to “one embodiment,” “anembodiment,” or similar language means that a particular feature,structure, or characteristic described in connection with the embodimentis included in at least one embodiment of the subject matter of thepresent disclosure. Appearances of the phrases “in one embodiment,” “inan embodiment,” and similar language throughout this specification may,but do not necessarily, all refer to the same embodiment. Similarly, theuse of the term “implementation” means an implementation having aparticular feature, structure, or characteristic described in connectionwith one or more embodiments of the subject matter of the presentdisclosure, however, absent an express correlation to indicateotherwise, an implementation may be associated with one or moreembodiments.

According to one general embodiment of an internal combustion enginesystem 100 shown in FIG. 1, the system includes an internal combustionengine 110 coupled to an exhaust system 120. The engine 110 is aspark-ignited engine fueled by gaseous hydrocarbons or fuel 140, such asnatural gas, petroleum gas (propane), and hydrogen. As defined herein,gaseous fuels, as opposed to non-gaseous liquid or aqueous fuels (e.g.,gasoline and diesel), are those that are introduced and managed withinthe engine in a gaseous state, as opposed to, a liquid state. Inspecific implementations, the engine 110 is a spark-ignited enginefueled by natural gas. Spark-ignited gaseous fuel engines are configuredand calibrated differently than spark-ignited non-gaseous fuel engines.Gaseous fuel engines introduce considerations not present withnon-gaseous engines. For example, non-gaseous engines do not producesignificant amounts of certain combustion byproducts produced by gaseousengines. Of particular relevance to the illustrated embodiments of thesystem 100 of the present disclosure, non-gaseous fuel engines produceno more than nominal amounts of methane compared to gaseous fuelengines, which produce large amounts of methane when the gaseous fuelitself contains a large amount of methane, which is normal with naturalgas and a wide variety of other gaseous fuels.

The internal combustion engine system 100 also includes an air intakesystem that receives and directs air into the engine 110. Accordingly,the air intake system includes an air inlet that is at essentiallyatmospheric pressure, thus enabling fresh air to enter the air system.In one embodiment, prior to the fresh air entering the engine 110, itreceives a metered amount of gaseous fuel 140. The quantity and timingof the gaseous fuel 140 added to the air is controlled by an electroniccontrol module 130 based on any of various operating conditions of theengine 100, such as engine speed, torque demand, air temperature andpressure, exhaust temperature and pressure, and the like. The gaseousfuel 140 can be stored in a storage tank and injected into the fresh airvia a fuel injector and fuel pump specifically configured to dose agaseous material. Although not shown, the fresh air may also be mixedwith recirculated exhaust gas from an exhaust gas recirculation (EGR)line. The fuel and air mixture may enter a compressor of a turbochargerbefore entering the engine. Alternatively, the gaseous fuel 140 can beadded to the air after the compressor. For example, in oneimplementation, the gaseous fuel 140 is directly injected into thecombustion chambers of the engine via a common rail and a plurality offuel injectors. Whether the fuel is injected directly into thecombustion chambers or injected into the air upstream of the engine, thecombined fuel and air mixture is ignited, and the fuel is combusted, viaa spark-ignition system to generate a pressure differential within thechambers for powering the engine.

Combustion of the gaseous fuel in the engine 110 produces exhaust gasthat is operatively vented to the exhaust system 120 after driving aturbine of a turbocharger in some implementations. Generally, theexhaust system 120 treats, regulates, and directs the exhaust gasreceived from the engine. The exhaust system 120 can include one or moreexhaust treatment components, such as, for example, three-way catalysts,oxidation catalysts, filters, adsorbers, and the like, for treating(i.e., removing pollutants from) the exhaust gas. Additionally, theexhaust system 120 can include exhaust flow regulation devices toregulate the exhaust gas flow rate and pressure (e.g., backpressure) ofexhaust gas flowing into, through, and out of the system 120. Also, theexhaust system 120 can include actuators and valves to direct exhaustgas to one or more destinations. For example, the exhaust system 120 caninclude an EGR valve that is actuatable to direct (e.g., vent) a portionof the received exhaust gas into the atmosphere as expelled exhaust anddirect a portion of the received exhaust gas into one or more EGR linesfor recirculation back into the combustion chambers.

The internal combustion engine system 100 also includes a sub-system fordithering liquid fuel 150 into the exhaust gas generated by the engine110 before the exhaust gas passes through the exhaust system 120.Although not shown, the liquid fuel 150 can stored in a storage tank andinjected into the exhaust gas via a fuel injector and fuel pumpspecifically configured to dose a liquid material. Generally, liquidmaterial injectors and pumps are able to more precisely, accurately, andresponsively administer doses of liquid material than gaseous materialinjectors and pumps. Moreover, liquid fuels, such as gasoline, have alower light-off temperature than gaseous fuels, such as natural gas.Accordingly, the liquid fuel added to the exhaust gas lowers thetemperature at which the oxidation of the exhaust gas occurs, whichleads to improved thermal management of the exhaust system.

As shown in FIG. 1, in certain embodiments, the liquid fuel 150 isinjected into the exhaust gas upstream of the exhaust system 120. Inother words, in certain embodiments, the liquid fuel 150 is configuredto be injected into the exhaust gas upstream of the exhaust treatmentcomponents of the exhaust system 120. The liquid fuel 150 can beinjected into the exhaust gas upstream of all exhaust treatmentcomponents, or downstream of some components and upstream of others.Generally, the liquid fuel 150 is injected upstream of the component orcomponents that utilize excess hydrocarbons in the exhaust gas toeffectuate desired results. For example, the excess hydrocarbonsgenerated by the injected liquid fuel 150 can be utilized by anoxidation catalyst to increase exhaust gas temperature or a three-waycatalyst to increase the NOx reduction efficiency of the exhaust system120.

The quantity and timing of the liquid fuel 150 dithered into the exhaustgas is controlled by the electronic control module 130 based on any ofvarious operating conditions of the engine 100, such as exhaust flowrate, exhaust temperature and pressure, exhaust air-to-fuel ratio,exhaust system operating conditions (e.g., NOx conversion capacity,oxygen storage capacity, and age of the system), and the like. In someimplementations, the electronic control module 130 controls theinjection of the gaseous fuel 140 into the engine independently of theinjection of the liquid fuel 150 into the exhaust system 120. In otherwords, the quantity and timing of the injection of liquid fuel 150 isnot dependent on the quantity and timing of the injection of the gaseousfuel 140. Generally, the electronic control module 130 communicates withand/or receives communication from various components of the system 100via electronic signals (as indicated by dashed lines). The electroniccontrol module 130 controls the operation of the engine system 100 andassociated sub-systems, such as the engine 110 and exhaust system 120.The electronic control module 130 is depicted in FIG. 1 as a singlephysical unit, but can include two or more physically separated units orcomponents in some embodiments if desired. In certain embodiments, theelectronic control module 130 receives multiple inputs, processes theinputs, and transmits multiple outputs. The multiple inputs may includesensed and/or calculated measurements from the sensors and various userinputs. The inputs are processed by the electronic control module 130using various algorithms, stored data, and other inputs to update thestored data and/or generate output values. The generated output valuesand/or commands are transmitted to other components of the controllerand/or to one or more elements of the engine system 10 to control thesystem to achieve desired results.

According to a specific embodiment, and referring to FIG. 2, theelectronic control module 130 includes an exhaust system conditionmodule 160 and a liquid fuel control module 164. Generally, the exhaustsystem condition module 160 and liquid fuel control module 164 cooperateto generate a liquid fuel dosing command 168 based on sensor inputs 166.The sensor inputs 166 may include measured or calculated conditions ofthe engine system 100 as discussed above. For example, in oneimplementation, the sensor inputs 166 include at least one of anair-to-fuel ratio input, a catalyst oxygen storage input, an exhausttemperature input, and an engine ON input. In some implementations, thesensor inputs 166 indicate only conditions of the engine systemdownstream of the engine 110 (e.g., solely based on conditions of theexhaust system 120). Based on the sensor inputs 166, the exhaust systemcondition module 160 determines an exhaust system condition 162 of theexhaust system 120. Generally, the exhaust system condition 162represents a condition of the exhaust system affected by the presence ofunburned hydrocarbons in the exhaust gas. In one implementation, theexhaust system condition 162 can be the exhaust gas temperature and/orthe NOx reduction efficiency of the exhaust system 120. Based on theexhaust system condition 162, the liquid fuel control module 164determines the quantity of liquid fuel necessary to achieve a desiredresult, and issues the liquid fuel dosing command 168, which commandsthe engine system 100 to inject the determined quantity of liquid fuelinto the exhaust gas at an appropriate time to realize the desiredresult.

In one implementation, the input includes one of an engine ON inputindicating the initiation of a cold start of the engine 110 and theexhaust system condition 162 is the exhaust gas temperature.Alternatively, the input includes a measurement from an exhausttemperature sensor. The liquid fuel control module 164 compares theexhaust gas temperature received from the exhaust system conditionmodule 160 to a corresponding predetermined threshold. If the exhaustgas temperature is below the threshold, the liquid fuel control module164 determines a quantity of liquid fuel necessary to reach the exhaustgas temperature threshold, and issues a liquid fuel dosing command 168corresponding with the determined quantity.

In another implementation, the input includes an air-to-fuel ratio inputand a catalyst oxygen storage input, and the exhaust system condition162 is the NOx reduction efficiency or performance of the exhaust system120. The air-to-fuel ratio input can be determined based on anestimation of the amount of oxygen and fuel in the exhaust gas based onknown operating conditions of the engine. The catalyst oxygen storageinput indicates the quantity of oxygen stored on an catalyst (e.g.,three-way catalyst) of the exhaust system 120, or the capacity of thecatalyst to store oxygen. The liquid fuel control module 164 comparesthe NOx reduction efficiency of the exhaust system 120 received from theexhaust system condition module 160 to a corresponding predeterminedthreshold. If the NOx reduction efficiency is below the threshold, theliquid fuel control module 164 determines a quantity of liquid fuelnecessary to reach the NOx reduction efficiency threshold, and issues aliquid fuel dosing command 168 corresponding with the determinedquantity.

Referring to FIG. 3, a specific embodiment of an internal combustionengine system 200 is shown. The engine system 200 is similar to theengine system 100 of FIG. 1, with like numbers and titles referring tolike features. Accordingly, unless otherwise indicated, the descriptionof the features of the engine system 100 applies equally to thecorresponding features of the engine system 200. Like the engine system100, the engine system 200 includes a gaseous fuel internal combustionengine 210 and an electronic control module 230. The engine 210 is aspark-ignited engine fueled by natural gas supplied from a natural gastank 240. The natural gas from the tank 240 is supplied to the engine210 via a natural gas injector 242 that is controlled by the electroniccontrol module 130. The natural gas is injected into the air before orafter the air enters the engine 210. The combusted natural gas producesexhaust gas that is received by an exhaust manifold 212 in exhaustreceiving communication with the engine 210. The engine 210 is inexhaust providing communication with an exhaust system that includes athree-way catalyst 220.

The three-way catalyst 220 can be a flow-through type catalyst having acatalyst bed exposed to the exhaust gas flowing through a main exhaustline of the exhaust system and past the bed. The catalyst bed includes acatalytic layer disposed on a washcoat or carrier layer. The carrierlayer can include any of various materials (e.g., oxides) capable ofsuspending the catalytic layer therein. The catalyst layer is made fromone or more catalytic materials selected to react with (e.g., oxidize)one or more pollutants in the exhaust gas. The catalytic materials ofthe three-way catalyst 220 can include any of various materials, such asprecious metals platinum, palladium, and rhodium, as well as othermaterials, such as transition metals cerium, iron, manganese, andnickel. Further, the catalyst materials can have any of various ratiosrelative to each other for oxidizing and reducing relative amounts andtypes of pollutants as desired.

Generally, the three-way catalyst 220 is so termed because it containscatalytic materials specifically selected to react with and oxidize orreduce three specific pollutants. The three specific pollutants includecarbon monoxide (CO), unburned hydrocarbons (UHC), and nitrogen oxides(NOx). In some implementations, the three-way catalyst 220 is housedwithin the same housing, and the catalyst includes three catalyst bedspositioned adjacent each other to form three separate catalyst stages.Although the three-way catalyst 220 is depicted as a single unit in FIG.3, in some embodiments, the three-way catalyst can be formed of two ormore separate, disparate units. For example, in one embodiment, thethree-way catalyst 220 is housed within a single housing, while inanother embodiment, the three-way catalyst 220 includes three separatecatalysts (e.g., a CO oxidation catalyst, a methane oxidation catalyst,and a NOx reduction catalyst) each housed within a separate housing. Inone embodiment, the NOx catalyst of the three-way catalyst 220 is a NOxadsorber catalyst. In another embodiment, the NOx catalyst of thethree-way catalyst 220 is a selective catalytic reduction (SCR) catalystthat forms part of a SCR system. Although not shown, the main exhaustline of the exhaust system may include other exhaust treatment devices,such as filters, that further treat the exhaust gas before it vents intothe atmosphere.

Like the engine system 100, the engine system 200 includes a sub-systemfor dithering gasoline into the exhaust gas generated by the engine 210before the exhaust gas enters the three-way catalyst 220. The gasolineis stored in a gasoline tank 250 and injected into the exhaust gas via agasoline injector 252, which can receive gasoline from the tank via afuel pump 254 operatively coupled with the engine 210. In theillustrated embodiment of FIG. 3, the gasoline injector 252 ispositioned such that gasoline is injected into the exhaust gas locatedwithin the exhaust manifold 212. Alternatively, the gasoline injector252 can be positioned downstream of the exhaust manifold 212 to injectgasoline into the exhaust gas downstream of the exhaust manifold. Thequantity and timing of the gasoline dithered into the exhaust gas iscontrolled by an electronic control module 230 Like the electroniccontrol module 130, the electronic control module 230 is configured todither gasoline directly into the exhaust gas on an as-needed basis topromote exhaust gas conditions conducive to achieving desired exhaustsystem performance.

According to certain implementations associated with an existinginternal combustion engine that has an exhaust system equipped with adiesel exhaust fluid (DEF) injection system, the components of the DEFinjection system can be utilized to inject gasoline (or other liquidfuel) instead of DEF. As mentioned above, certain internal combustionengine systems have an exhaust aftertreatment system with a selectivecatalytic reduction (SCR) system configured to reduce NOx on an SCRcatalyst in the presence of ammonia. The ammonia is introduced into theexhaust gas stream in the form of an aqueous reductant, such as urea,that decomposes into ammonia after being injected into an exhaust gasstream. The aqueous reductant is stored in a reductant storage tank. Insome implementations, each internal combustion engine system 100, 200can be an internal combustion engine system with a DEF injection systemthat has been retrofitted to inject a liquid fuel instead of DEF. Forexample, the DEF injection system can be evacuated of DEF by, amongother things, emptying DEF from the DEF storage tank. Then, the DEFstorage tank can be filled with aqueous fuel. Because DEF is in a liquidor aqueous state, the components of the DEF injection system (e.g.,storage tank, pump, injector, delivery lines, etc.) are conducive tohandling liquid or aqueous fuel. Accordingly, a DEF injection system canbe easily retrofitted to handle and inject a liquid fuel withoutsubstantial modifications, if any, to the structural components of theDEF injection system. In certain implementations, the DEF injectioncontrol system, including injection algorithms and mapping, is replacedwith a liquid fuel injection control system as part of the retrofit.

The exhaust system may include an oxygen storage capacity (OSC) sensor222 and an air-to-fuel ratio sensor 224 configured to calculate anddetect, respectively, the OSC of the three-way catalyst 220 and theair-to-fuel ratio of exhaust gas entering the three-way catalyst. TheOSC sensor 222 can be a virtual sensor that estimates the OSC of thethree-way catalyst 220 based on various sensed and/or estimated inputs.In one implementation, the OSC of the three-way catalyst 220 isdetermined based on a difference between the air-to-fuel ratio of theexhaust gas upstream and downstream of the three-way catalyst. Thedetermination of the OSC by the OSC sensor 22 can be further based onthe application of the air-to-fuel ratio difference to a three-waycatalyst model 228 that models the behavior of the three-way catalyst220. The air-to-fuel ratio of exhaust gas downstream of the three-waycatalyst can be determined by an air-to-fuel sensor 226. The air-to-fuelsensors 224, 226 can be a physical sensor that detects the air-to-fuelratio of the exhaust gas. The OSC sensor 222 and air-to-fuel ratiosensor 224 are in electronic communication with the electronic controlmodule 230 to supply the electronic control module with the calculatedand detected OSC of the three-way catalyst 220 and the air-to-fuel ratioof the exhaust gas. The exhaust system condition module of theelectronic control module 230 utilizes the OSC and air-to-fuel ratioinputs from the sensors 222, 224 to determine an exhaust systemcondition as described above. The electronic control module 230 also hasa gasoline control module that utilizes the exhaust system condition togenerate a gasoline dosing command that commands actuation of thegasoline injector 252 to inject a desired amount of gasoline into theexhaust gas.

Referring to FIG. 4, according to one embodiment, a method 300 fordithering liquid fuel into an exhaust system of an internal combustionengine system is shown. In certain implementations, each of theelectronic control modules 130, 230 may be configured to execute thesteps of the method 300. The method 310 starts by determining whether anexisting DEF injection system is being retrofitted for liquid fuelinjection at 310. If the determination at 310 is answered affirmatively,then the method 300 replaces the DEF in the DEF injection system with aliquid fuel, such as gasoline, at 320. Should an internal combustionengine system be equipped with a liquid fuel injection system such thatthe determination at 320 is answered in the negative, or after replacingDEF in an existing DEF injection system with liquid fuel at 320, themethod 300 proceeds to determine one or more operating conditions of theexhaust system, as well as in some implementations one or more operatingconditions of the engine, at 330. The operating conditions of theexhaust system may include the air-to-fuel ratio of the exhaust and/orthe OSC of an oxidation catalyst. The operating conditions of the enginemay include engine speed and cold-start conditions. Based on theoperating conditions of the exhaust system, and engine system in someimplementations, the method 300 dithers the liquid fuel into the exhaustsystem (e.g., the exhaust gas upstream of exhaust treatment componentsof the exhaust system) at 340. Generally, the method 300 dithers liquidfuel into the exhaust system at 340 to facilitate more efficientreduction of NOx in the exhaust gas and/or improve thermal management ofthe exhaust gas.

Although mentioned above, the liquid fuel dithering systems, apparatus,and methods provides one or more advantages over conventional systems.For example, in some implementations, the liquid fuel dithering systems,apparatus, and methods of the present disclosure may provide one or moreof the following advantages additional advantages: (1) fewer constraintson engine performance and tuning as liquid fuel is dithered downstreamof engine; (2) smaller oxidation catalysts as less oxygen is required tobe stored when engine is running leaner; (3) lower oxidation catalystcost because fewer precious metals or catalytic materials are required;(4) reduction in methane emissions; and (5) improved response undertransient operating conditions of the engine.

As will be appreciated by one skilled in the art, aspects of the presentinvention may be embodied as a system, method, and/or computer programproduct. Accordingly, aspects of the present invention may take the formof an entirely hardware embodiment, an entirely software embodiment(including firmware, resident software, micro-code, etc.) or anembodiment combining software and hardware aspects that may allgenerally be referred to herein as a “circuit,” “module,” or “system.”Furthermore, aspects of the present invention may take the form of acomputer program product embodied in one or more computer readablemedium(s) having program code embodied thereon.

Many of the functional units described in this specification have beenlabeled as modules, in order to more particularly emphasize theirimplementation independence. For example, a module may be implemented asa hardware circuit comprising custom VLSI circuits or gate arrays,off-the-shelf semiconductors such as logic chips, transistors, or otherdiscrete components. A module may also be implemented in programmablehardware devices such as field programmable gate arrays, programmablearray logic, programmable logic devices or the like.

Modules may also be implemented in software for execution by varioustypes of processors. An identified module of program code may, forinstance, comprise one or more physical or logical blocks of computerinstructions which may, for instance, be organized as an object,procedure, or function. Nevertheless, the executables of an identifiedmodule need not be physically located together, but may comprisedisparate instructions stored in different locations which, when joinedlogically together, comprise the module and achieve the stated purposefor the module.

Indeed, a module of program code may be a single instruction, or manyinstructions, and may even be distributed over several different codesegments, among different programs, and across several memory devices.Similarly, operational data may be identified and illustrated hereinwithin modules, and may be embodied in any suitable form and organizedwithin any suitable type of data structure. The operational data may becollected as a single data set, or may be distributed over differentlocations including over different storage devices, and may exist, atleast partially, merely as electronic signals on a system or network.Where a module or portions of a module are implemented in software, theprogram code may be stored and/or propagated on in one or more computerreadable medium(s).

The computer readable medium may be a tangible computer readable storagemedium storing the program code. The computer readable storage mediummay be, for example, but not limited to, an electronic, magnetic,optical, electromagnetic, infrared, holographic, micromechanical, orsemiconductor system, apparatus, or device, or any suitable combinationof the foregoing.

More specific examples of the computer readable storage medium mayinclude but are not limited to a portable computer diskette, a harddisk, a random access memory (RAM), a read-only memory (ROM), anerasable programmable read-only memory (EPROM or Flash memory), aportable compact disc read-only memory (CD-ROM), a digital versatiledisc (DVD), an optical storage device, a magnetic storage device, aholographic storage medium, a micromechanical storage device, or anysuitable combination of the foregoing. In the context of this document,a computer readable storage medium may be any tangible medium that cancontain, and/or store program code for use by and/or in connection withan instruction execution system, apparatus, or device.

The computer readable medium may also be a computer readable signalmedium. A computer readable signal medium may include a propagated datasignal with program code embodied therein, for example, in baseband oras part of a carrier wave. Such a propagated signal may take any of avariety of forms, including, but not limited to, electrical,electro-magnetic, magnetic, optical, or any suitable combinationthereof. A computer readable signal medium may be any computer readablemedium that is not a computer readable storage medium and that cancommunicate, propagate, or transport program code for use by or inconnection with an instruction execution system, apparatus, or device.Program code embodied on a computer readable signal medium may betransmitted using any appropriate medium, including but not limited towire-line, optical fiber, Radio Frequency (RF), or the like, or anysuitable combination of the foregoing

In one embodiment, the computer readable medium may comprise acombination of one or more computer readable storage mediums and one ormore computer readable signal mediums. For example, program code may beboth propagated as an electro-magnetic signal through a fiber opticcable for execution by a processor and stored on RAM storage device forexecution by the processor.

Program code for carrying out operations for aspects of the presentinvention may be written in any combination of one or more programminglanguages, including an object oriented programming language such asJava, Smalltalk, C++, PHP or the like and conventional proceduralprogramming languages, such as the “C” programming language or similarprogramming languages. The program code may execute entirely on theuser's computer, partly on the user's computer, as a stand-alonesoftware package, partly on the user's computer and partly on a remotecomputer or entirely on the remote computer or server. In the latterscenario, the remote computer may be connected to the user's computerthrough any type of network, including a local area network (LAN) or awide area network (WAN), or the connection may be made to an externalcomputer (for example, through the Internet using an Internet ServiceProvider).

The computer program product may be shared, simultaneously servingmultiple customers in a flexible, automated fashion. The computerprogram product may be standardized, requiring little customization andscalable, providing capacity on demand in a pay-as-you-go model.

The computer program product may be stored on a shared file systemaccessible from one or more servers. The computer program product may beexecuted via transactions that contain data and server processingrequests that use Central Processor Unit (CPU) units on the accessedserver. CPU units may be units of time such as minutes, seconds, hourson the central processor of the server. Additionally the accessed servermay make requests of other servers that require CPU units. CPU units arean example that represents but one measurement of use. Othermeasurements of use include but are not limited to network bandwidth,memory usage, storage usage, packet transfers, complete transactionsetc.

Aspects of the embodiments may be described above with reference toschematic flowchart diagrams and/or schematic block diagrams of methods,apparatuses, systems, and computer program products according toembodiments of the invention. It will be understood that each block ofthe schematic flowchart diagrams and/or schematic block diagrams, andcombinations of blocks in the schematic flowchart diagrams and/orschematic block diagrams, can be implemented by program code. Theprogram code may be provided to a processor of a general purposecomputer, special purpose computer, sequencer, or other programmabledata processing apparatus to produce a machine, such that theinstructions, which execute via the processor of the computer or otherprogrammable data processing apparatus, create means for implementingthe functions/acts specified in the schematic flowchart diagrams and/orschematic block diagrams block or blocks.

The program code may also be stored in a computer readable medium thatcan direct a computer, other programmable data processing apparatus, orother devices to function in a particular manner, such that theinstructions stored in the computer readable medium produce an articleof manufacture including instructions which implement the function/actspecified in the schematic flowchart diagrams and/or schematic blockdiagrams block or blocks.

The program code may also be loaded onto a computer, other programmabledata processing apparatus, or other devices to cause a series ofoperational steps to be performed on the computer, other programmableapparatus or other devices to produce a computer implemented processsuch that the program code which executed on the computer or otherprogrammable apparatus provide processes for implementing thefunctions/acts specified in the flowchart and/or block diagram block orblocks.

The schematic flowchart diagrams and/or schematic block diagrams in theFigures illustrate the architecture, functionality, and operation ofpossible implementations of apparatuses, systems, methods and computerprogram products according to various embodiments of the presentinvention. In this regard, each block in the schematic flowchartdiagrams and/or schematic block diagrams may represent a module,segment, or portion of code, which comprises one or more executableinstructions of the program code for implementing the specified logicalfunction(s).

It should also be noted that, in some alternative implementations, thefunctions noted in the block may occur out of the order noted in theFigures. For example, two blocks shown in succession may, in fact, beexecuted substantially concurrently, or the blocks may sometimes beexecuted in the reverse order, depending upon the functionalityinvolved. Other steps and methods may be conceived that are equivalentin function, logic, or effect to one or more blocks, or portionsthereof, of the illustrated Figures.

Although various arrow types and line types may be employed in theflowchart and/or block diagrams, they are understood not to limit thescope of the corresponding embodiments. Indeed, some arrows or otherconnectors may be used to indicate only the logical flow of the depictedembodiment. For instance, an arrow may indicate a waiting or monitoringperiod of unspecified duration between enumerated steps of the depictedembodiment. It will also be noted that each block of the block diagramsand/or flowchart diagrams, and combinations of blocks in the blockdiagrams and/or flowchart diagrams, can be implemented by specialpurpose hardware-based systems that perform the specified functions oracts, or combinations of special purpose hardware and program code.

Instances in this specification where one element is “coupled” toanother element can include direct and indirect coupling. Directcoupling can be defined as one element coupled to and in some contactwith another element. Indirect coupling can be defined as couplingbetween two elements not in direct contact with each other, but havingone or more additional elements between the coupled elements. Further,as used herein, securing one element to another element can includedirect securing and indirect securing. Additionally, as used herein,“adjacent” does not necessarily denote contact. For example, one elementcan be adjacent another element without being in contact with thatelement.

As used herein, the phrase “at least one of”, when used with a list ofitems, means different combinations of one or more of the listed itemsmay be used and only one of the items in the list may be needed. Theitem may be a particular object, thing, or category. In other words, “atleast one of” means any combination of items or number of items may beused from the list, but not all of the items in the list may berequired. For example, “at least one of item A, item B, and item C” maymean item A; item A and item B; item B; item A, item B, and item C; oritem B and item C. In some cases, “at least one of item A, item B, anditem C” may mean, for example, without limitation, two of item A, one ofitem B, and ten of item C; four of item B and seven of item C; or someother suitable combination.

In the above description, certain terms may be used such as “up,”“down,” “upper,” “lower,” “horizontal,” “vertical,” “left,” “right,”“over,” “under” and the like. These terms are used, where applicable, toprovide some clarity of description when dealing with relativerelationships. But, these terms are not intended to imply absoluterelationships, positions, and/or orientations. For example, with respectto an object, an “upper” surface can become a “lower” surface simply byturning the object over. Nevertheless, it is still the same object.Further, the terms “including,” “comprising,” “having,” and variationsthereof mean “including but not limited to” unless expressly specifiedotherwise. An enumerated listing of items does not imply that any or allof the items are mutually exclusive and/or mutually inclusive, unlessexpressly specified otherwise. The terms “a,” “an,” and “the” also referto “one or more” unless expressly specified otherwise. Further, the term“plurality” can be defined as “at least two.”

The subject matter of the present disclosure may be embodied in otherspecific forms without departing from its spirit or essentialcharacteristics. The described embodiments are to be considered in allrespects only as illustrative and not restrictive. The scope of theinvention is, therefore, indicated by the appended claims rather than bythe foregoing description. All changes which come within the meaning andrange of equivalency of the claims are to be embraced within theirscope.

What is claimed is:
 1. An internal combustion engine system, comprising:a spark-ignited internal combustion engine powered by a gaseous fuel; anexhaust system in exhaust gas receiving communication with the internalcombustion engine, the exhaust system comprising an exhaust treatmentcomponent; and a liquid fuel injection system in liquid fuel injectingcommunication with the exhaust system to inject liquid fuel into exhaustgas upstream of the exhaust treatment component.
 2. The internalcombustion engine system of claim 1, wherein the gaseous fuel comprisesnatural gas.
 3. The internal combustion engine system of claim 1,wherein the liquid fuel comprises gasoline.
 4. The internal combustionengine system of claim 1, wherein the liquid fuel injection systeminjects liquid fuel into the exhaust gas based on an air-to-fuel ratioof the exhaust gas generated by the spark-ignited internal combustionengine.
 5. The internal combustion engine system of claim 1, wherein thespark-ignited internal combustion engine generates exhaust gas with anair-to-fuel ratio above 1.0.
 6. The internal combustion engine system ofclaim 1, wherein the exhaust treatment component stores oxygen, andwherein the liquid fuel injection system injects liquid fuel into theexhaust gas based on an oxygen storage capacity of the exhaust treatmentcomponent.
 7. The internal combustion engine system of claim 1, whereinthe liquid fuel injection system injects liquid fuel into the exhaustgas during a cold start of the spark-ignited internal combustion engine.8. The internal combustion engine system of claim 1, wherein the exhaustsystem comprises an exhaust manifold coupled to the spark-ignitedinternal combustion engine, and wherein the liquid fuel injection systeminjects liquid fuel into the exhaust manifold.
 9. The internalcombustion engine system of claim 1, further comprising a gaseous fuelinjection system in gaseous fuel injecting communication with thespark-ignited internal combustion engine, wherein the liquid fuelinjection system injects liquid fuel into the exhaust gas independentlyof the injection of gaseous fuel injected into the engine by the gaseousfuel injection system.
 10. The internal combustion engine system ofclaim 1, wherein quantity and timing of the injection of liquid fuelinto the exhaust gas by the liquid fuel injection system is based solelyon conditions of the internal combustion engine system downstream of thespark-ignited internal combustion engine.
 11. The internal combustionengine system of claim 1, wherein the exhaust treatment componentcomprises an oxidation catalyst.
 12. The internal combustion enginesystem of claim 1, wherein the exhaust treatment component comprises athree-way catalyst.
 13. The internal combustion engine system of claim1, wherein the liquid fuel injection system comprises a retrofitteddiesel exhaust fluid injection system.
 14. The internal combustionengine system of claim 1, wherein the exhaust treatment componentcomprises a nitrogen oxide reduction catalyst.
 15. The internalcombustion engine system of claim 1, wherein the gaseous fuel comprisessubstantially solely natural gas.
 16. An electronic control module for aspark-ignited internal combustion engine powered by a gaseous fuel,comprising: an exhaust system condition module that determines acondition of an exhaust system in exhaust gas receiving communicationwith the spark-ignited internal combustion engine; and a liquid fuelcontrol module that commands the dithering of a liquid fuel into theexhaust system based on the condition of the exhaust system.
 17. Theelectronic control module of claim 16, wherein the exhaust systemcomprises an oxidation catalyst, and wherein the condition of theexhaust system comprises an oxygen storage capacity of the oxidationcatalyst.
 18. The electronic control module of claim 16, wherein thecondition of the exhaust system comprises an air-to-fuel ratio ofexhaust gas generated by the spark-ignited internal combustion engine.19. The electronic control module of claim 16, wherein the condition ofthe exhaust system comprises an exhaust gas temperature below a minimumthreshold.
 20. A method for dithering a liquid fuel into an exhaustsystem in exhaust receiving communication with a spark-ignited internalcombustion engine powered by a gaseous fuel, the method comprising:determining a condition of the exhaust system; and injecting a liquidfuel into exhaust gas flowing through the exhaust system based on thecondition of the exhaust system.